The present invention relates generally to a method and apparatus for the hydrogenation or liquefaction of coal, and more particularly to such a method and apparatus capable of continuously converting coal particulates to primarily liquid hydrocarbon products by providing an aqueous pumpable slurry containing coal and a water soluble catalyst, forming agglomerates of the coal with the aid of added oil, separating essentially all the water from the agglomerates by passing the agglomerates through a drainage means followed by a dryer and preheater, and then passing the dried and preheated agglomerates into a reactor where they are hydrogenated.
In continuous direct coal liquefaction processes as previously known, pulverized coal is fed into the process as a slurry formed of coal particles and a solvent provided by recycling a portion of the coal liquefaction product. The coal slurry is usually pressurized by a pump, passed through a preheater and then into a reactor where the coal is converted to liquid and gaseous products under the influence of elevated temperature and hydrogen pressure. These previous processes are generally disclosed in U.S. Pat. Nos. 3,519,555; 3,700,584; 3,791,957; 4,089,658; and 4,111,788. The maximum solids content of the feed slurry in such previous processes is limited to slightly more than 40 weight percent since with greater solids content the slurry becomes so viscous as to be unpumpable. The use of such relatively large concentrations of solvent with the feed coal is disadvantageous in that it is wasteful of energy since the solvent must be heated to reaction temperature along with the coal and is also wasteful of the interior volume of process equipment in that only about 50 percent or less by volume of the feed slurry consists of coal. Thus, it is desirable to have an alternative method to the conventional coal/solvent slurry for feeding coal to a liquefaction process.
It is also known within the art that an efficient method for introducing catalysts into a coal liquefaction system is through impregnation from solution. The catalysts are often salts of transition metals such as iron, molybdenum, nickel or tin. If water-soluble salts are used, the catalysts may be impregnated from an aqueous solution. Compared to other methods of catalyst addition, impregnated catalysts are efficacious at small concentrations, which is thought to be due to the highly dispersed nature of the catalysts within the coal particles and the proximity of catalysts to reactive sites in the coal. The use of catalyst impregnation in continuous liquefaction processes has been limited to date due to the expense of drying coal after impregnation and prior to charging a coal-solvent slurry to the process.
The direct liquefaction of coal in the presence of large amounts of water is also known in the art. Batchwise reactions have been carried out using ratios of coal-to-water that could be obtained from a pumpable slurry of coal and water as described in several papers published in the Proceedings of the 1985 International Conference on Coal Science (Pergamon Press) which are entitled "Oxygen Loss and Conversion of Coal" by Ross and Hum, "Novel Liquefaction Solvent; H.sub.2 O-H.sub.2 S" by Stenberg and Nowak, and "Prospects for Coal Liquefaction Using an Aqueous Feed Stream" by Ruether et al. A major disadvantage to carrying out liquefaction in the presence of large quantities of water is due to the contribution of the vapor pressure of water to the total system pressure. Typically such liquefaction is carried out at a total pressure in the vicinity of 4,000 psig or higher which is not economically attractive. Thus, to the present time there is no commercially attractive method for liquifying coal that uses an aqueous feed slurry.